♻️ refactor(test): 清理文件集成测试中的未使用变量

- 移除未使用的mockDataSource变量，减少测试代码冗余
- 简化测试前置设置，提高测试代码可读性

src/server/api/files/__tests__/files.integration.test.ts

@@ -10,7 +10,6 @@ vi.mock('@/server/middleware/auth.middleware');
 
 describe('File API Integration Tests', () => {
   let client: ReturnType<typeof testClient<typeof fileApiRoutes>>['api']['v1'];
-  let mockDataSource: DataSource;
   const user1 = {
     id: 1,
     username: 'testuser',
@@ -36,8 +35,6 @@ describe('File API Integration Tests', () => {
   beforeEach(async () => {
     vi.clearAllMocks();
 
-    mockDataSource = {} as DataSource;
-
     // Mock auth middleware to bypass authentication
     vi.mocked(authMiddleware).mockImplementation(async (_, next) => {
       _.set('user', user1)